1. Field of the Invention
The present invention relates to fuses for protecting electrical circuits from high-current levels and, more particularly, to a fuse element that is made from a composition of conductive and arc suppressing materials.
2. Description of Related Art
Our contemporary society enjoys the convenience and utility offered by the plethora of modern electronic devices available to industry, businesses and consumers. Electronic devices, however, often contain circuitry or components that may be sensitive to certain levels of current. Spikes or otherwise higher-than-nominal current levels are often referred to as over-current conditions. The occurrence of over-current conditions may result in damage to or destruction of the circuitry or components of the electronic device. As a result, designers often utilize fuses to shield the circuitry from such conditions.
Fuses are well known and widely used for over-current protection of electronic circuits. Many current limited fuses are made of metal wires, metal sheets, or metal films as the fusing elements. When the electrical current passing through the fusing element exceeds a certain level, the heat generated by the electrical current will melt the fusing element and create an open circuit, thereby preventing further current flow. Occasionally, however, when the fuse element melts and vaporizes, arcing occurs. It can allow undesired current levels to reach the circuit to be protected, potentially causing damage to the circuit. Therefore, the fusing elements are typically surrounded by arc suppressing or arc shielding materials. Many types and designs of such fuses are known in the art and such fuses are described, for example, in U.S. Pat. Nos: 6,590,490; 6,005,470; 5,726,621; 5,479,147; 5,453,726; 5,296,833; 5,245,308; 5,228,188; and 2,864,917.
A good fuse should have good arc suppressing capability by quenching the arc in a short time. In order to quench or suppress the arc, several materials, like ceramic powder, glass, organic materials, etc, are used to enclose the fusing elements. These arc-suppressing materials absorb the metal vapor created by the melting/vaporizing fuse element and cut off the current through the arc. Currently, arc suppressing materials are used in locations surrounding the fusing elements in many commercially available fuses. One limitation of such conventional fuse designs, however, is the limited contact surface area between the fuse element and the arc suppressing material(s). Because of the limited contact surface area between the conductive material(s) and surrounding arc suppressing material(s), the time it takes for the arc suppressing materials to cut off or quench an arc resulting from a high current load on the fuse element may be unduly long, potentially allowing high current levels to reach an electronic circuit or component to be protected. Thus, a larger contact surface area between the conductive material of a fuse element and an arc suppressing material is desirable for better and faster arc quenching.